Substance abuse and HIV-1 infection are highly comorbid, and HIV-1 infection correlates with the progression of neuropsychological dysfunctions identified as NeuroAIDS. However, relatively little is known about HIV modulation of the rewarding effects of abused drugs. Biological mechanisms linking HIV-related neuropathology to neural dysfunction and the progression of behavioral abnormalities in vivo are not well understood. Recent epidemiological evidence suggests that the HIV regulatory protein Tat and other HIV-proteins may spread throughout the brain from HIV-infected cells, inducing neuronal dysfunction that could account for behavioral changes. We hypothesize that exposure to Tat exerts neurochemical changes in forebrain circuitry mediating reward, thereby potentiating morphine's rewarding effects. This proposal utilizes the GT-tg transgenic mouse and its conditional gene induction strategy via doxycycline (Dox) administration, which enables controlled, brain-selective expression of Tat protein, to assess Tat effects on opioid-related effects and behaviors. Dox-induced GT-tg bigenic mice will be studied to assess whether Tat potentiates morphine conditioned-place preference (CPP) and voluntary morphine consumption (using a two-bottle choice (TBC) assay) compared to mice lacking Tat. Additional studies will evaluate Tat-induced reinstatement of extinguished morphine-seeking behavior. We will also use magnetic resonance spectroscopy (MRS) to determine whether Tat protein alters medial frontal cortex glutamate and N-acetylaspartate levels, which could reflect altered neurotransmission and neurotoxicity. Lastly, we will use behavioral and MRS methodology to assess whether the anti-inflammatory agent indomethacin, the NMDA-receptor (NR2B-selective) antagonist ifenprodil, or the small molecule Tat protein inhibitor didehydro-Cortistatin (dCA) can inhibit or reverse Tat-mediated effects. Tat protein expression in postmortem brain samples after treatment and testing will be confirmed by ELISA and Western blot analysis. Our pilot behavioral data suggest that Tat both potentiates morphine-CPP and induces reinstatement of extinguished morphine-seeking behavior. Pilot MRS studies of medial frontal cortex found decreases in glutamate and N-acetylaspartate in Dox-treated GT-tg mice versus baseline measures in these mice. Pilot data also suggest that prophylactic pretreatment with indomethacin and dCA prevented Tat-induced potentiation of morphine CPP. Overall, this project is designed to extend pilot findings, and lead to a better understanding of how Tat contributes to the neuropathology produced during HIV infection, including the possible modulation of behavioral motivation for opioids. Study findings may also identify novel mechanisms that could be exploited as therapeutic interventions for development to treat comorbid HIV/opioid abuse.